Semiconductor integrated circuits are formed using large numbers of complex processing operations to form several layers of devices and electrical connections stacked on top of each other. Isolating layers of dielectric material are needed to electrically isolate semiconductor devices and electrical connecting lines from each other. The dielectric material is typically deposited in lateral spaces between elements such as semiconductor devices and between electrical connections such as trace lines. The dielectric material is also deposited between multiple layers of devices or connections to isolate portions of layers from each other.
FIG. 1 shows an integrated circuit 100, including a semiconductor substrate 110. The integrated circuit 100 includes a number of semiconductor devices 120 that are formed on, or within the substrate 110. Electrical connections such as first electrical connection 130 and second electrical connection 132 are included for interconnecting selected semiconductor devices 120.
Current fabrication methods utilize a multiple step process to isolate various elements of the integrated circuit 100 as described. A first dielectric layer 150 is included in the multiple step process. The first dielectric layer 150 is shown in FIG. 1 located over the electrical connections 130 and 132. The dielectric layer 150 in common configurations is a conformal layer that contacts both a substrate elevation level area 112 and an element elevation level area 114.
One current technique also utilizes supplemental structures such as structure 140 to minimize the amount of surface area on the substrate 110 that is at the substrate elevation level 112. However, with the configuration shown in FIG. 1, there is still a substantial difference in elevation between the substrate elevation level 112 and the element elevation level 114. The conformal dielectric layer 150 of the current process does not yield a planar outer surface.
It is desirable to form a substantially planar outer surface so that stacks of layers including subsequent semiconductor devices or electrical connections can be formed as needed. Using the current process, additional dielectric layers such as second dielectric layer 160 are needed to form a substantially planar outer surface 162. The outer surface 162 is made planar by selecting the second dielectric material and deposition process such that remaining recesses 163 are filled in.
Currently, no process or product exists that forms the substantially planar outer surface 162 in a single processing operation, with a single layer of material. Multiple process operations, while often necessary, are undesirable because of added time and manufacturing cost associated with each additional operation.
A via 170 is further shown in FIG. 1, formed through the first dielectric layer 150 and the second dielectric layer 160. The via 170 is needed when utilizing subsequent device or electrical connection layers, to form an electrical contact that communicates with, for example, the second electrical connection 132 as shown.
The via 170 includes a via width 172. Because the via 170 passes through both the first dielectric layer 150 and the second dielectric layer 160 in order to reach the second electrical connection 132, the via has a height that is equal to a thickness 166. The thickness 166 is equal to a first dielectric layer thickness 152 added to a second dielectric layer thickness 164. The via 170 has an aspect ratio equal to its height over its width 172. Due to thickness variations introduced in each deposition operation, there is a large variation in aspect ratios of vias formed after two dielectric depositions. High aspect ratio vias can be difficult to fill with conductive material in later processing operations. Aspect ratio variations are thus undesirable because of the resulting low reliability of high aspect ratio vias.
What is needed is a method of processing a semiconductor wafer to form a semiconductor device or integrated circuit that uses fewer processing steps. What is also needed is a method of processing a semiconductor wafer to form a semiconductor device or integrated circuit that allows more controlled variation of via aspect ratios.